Hazardous wastes, including solid and liquid wastes, by definition contain constituents that are believed to be hazardous either to human health or to the environment. In the United States, these wastes are regulated under the Resource Conservation and Recovery Act (RCRA). In order to dispose of such wastes, the wastes typically have to be treated according to some type of remediation process in order to remove or render harmless some of the hazardous components. In most instances, the wastes are not recycled but, instead, end up in landfills.
Many of the hazardous components that must either be removed or render harmless in a waste stream include most of the heavy metals, which are commonly defined as metals having an atomic weight exceeding about 18. In particular, RCRA has set leaching limits for various regulated metals which include arsenic, cadmium, lead, zinc, chromium, copper, barium, etc.
Some remediation processes have proven to be successful in removing hazardous components particularly from gaseous wastes, and some liquid wastes. A need remains, however, for a remediation process for removing solid contaminants contained in solid wastes and wastes that comprise a mixture of liquids and solids. In the past, remediation processes have included, for instance, soil washing, bioremediation, and incineration. Unfortunately, these processes are somewhat contaminant specific and limited to a certain range of organic or metallic substances. Further, the remediated waste, although perhaps clean enough from a risk-based standpoint, is typically unusable for a business or commercial application. In this regard, the residual waste typically ends up in a landfill, but only if the waste material can meet metals leaching criteria, which can be difficult.
Besides incineration, soil washing and bioremediation, vitrification has also been proposed in the past as a process to remediate hazardous wastes. In general, vitrification refers to a process by which a material is heated above its fusion temperature in order to produce a ceramic or glassy material, such as oxides of silicon, calcium, or aluminum. In the past, vitrification has been used to treat hazardous constituents, such as heavy metals, by encouraging the constituents to become a part of the molecular structure of the vitrified matter. In other words, the hazardous constituents have been encapsulated within the glassy materials in order to attempt to prevent the hazardous constituents from leaching out or otherwise entering the environment. Unfortunately, however, those attempting to practice this process have found it extremely difficult to consistently meet leaching criteria for safe disposable of the materials.
In view of these deficiencies, recent attention has been focused on not encapsulating the hazardous components, but instead separating them from the remainder of the materials. For instance, in U.S. Pat. No. 5,612,008 to Kirk, et al., a process for treating solid wastes containing inorganic contaminants is disclosed. In the process disclosed in Kirk, et al., volatilizable inorganic contaminants are removed from solid wastes by heating the waste to a temperature sufficiently high for volatilization of the inorganic contaminants to occur and sufficiently low so as to prevent vitreous matter or slag formation of the solid waste. In particular, in Kirk, et al., it is important that slag not form due to the large energy requirements and due to the handling problems that may occur. In Kirk, et al., however, not all of the contaminants are vaporized and thus residual amounts of contaminants remain in the resulting material. Thus, the resulting material has limited uses.
In view of the above, a need still remains for a process whereby hazardous contaminants, particularly inorganic compounds such as heavy metals, can be separated and removed from a waste material. A need also exists for such a process in which the remaining material is substantially free of hazardous constituents and thus can be recovered, recycled, and used in any desired application.